Remove TWebFile access for http(s) TURLs and use default TFile::Open via davix instead

Remove the old TWebFile access for http(s) TURLs in GaudiSvc/src/FileMgr/RootFileHandler.cpp. Use the default TFile::Open method that triggers the proper davix usage instead.

There was not objection within ATLAS and I am not sure if there is actually a remaining use-case for the current TWebFile method in this case, so I using this MR to find out.

Tagging @leggett, @ssnyder, @akraszna, @mnowak for info.